Traditionally, a sample of material would have been removed during processing from a process system and then analysed. It will be appreciated that techniques requiring the removal of material from a process system for separate analysis are both labour-intensive and time consuming.
More recently, techniques have been developed which allow material to be analysed on-line. One such device is disclosed in WO 99/32872. This document discloses a device for use in and a method of sampling material on-line in a process system which comprises a sample collector in which in use a sample of material is collected and a measuring device for taking measurements from the collected sample. The device further comprises a sample displacing means for displacing the collected sample from the sample collector so that the sample collector can receive a new sample of material. The sample displacing means comprises a pressurised gas supply, which in use is actuated to displace the collected sample and a small bore tube for leading the pressurised gas from the pressure gas source to the sample collector.
Ordinarily, this device has been found to operate satisfactorily. However, occasionally, it has been found that the sample collector is not completely emptied before receiving a new sample. Material properties of the sample, like binding forces can make it difficult to break up the sample and empty the sample collector. In some cases, sample particles have a sticky surface and tend to stick to each other or to the surface of the sample collector. It will be appreciated that even small residues of the previous sample in the sample collector are undesirable as they might influence the measurement on the next sample.
Another sampling apparatus is known from U.S. Pat. No. 5,750,996. In this document an apparatus and method for non-destructive inspection of a coated article is described. The apparatus comprises a probe, which has a recess for receiving coated article and a communicating fiberoptic receiving passageway. To displace the coated article from the recess, pressurised air is supplied to the lower portion of the recess to thereby urge the coated article out of the recess.
A drawback with the device described in U.S. Pat. No. 5,750,996 is that it is difficult to completely empty the recess of coated article. A further drawback is that the outlet for pressurised air might get clogged as particles fall down into the outlet due to its position in the bottom of the recess.